When a booking ends, check whether it was the customer's first booking with us. If it wasn't, or if we've already emailed them about a review, do nothing.
Otherwise, email them a short thank-you for visiting, name the location they booked, and ask them to leave a review on Google: [your Google review link].
Keep it warm and under 70 words, write in the customer's language, and don't offer anything in return for the review.